A. Field of the Invention
This invention relates to the mechanical aspects of a unitary device containing electronic components, referred to herein generically as a "chassis". Some examples are devices containing communications equipment and used by telephone companies, internet service providers, computer network operators, and other types of users. The features of the present invention contain any fire that may occur within the chassis and prevent flames from migrating out of the chassis into the enviromnent, while preserving airflow through the chassis to keep the chassis cool during periods of normal operation.
B. Description of Related Art
Integrated telecommunications devices, such as routers, switches, network access servers, remote access concentrators, TI span termination shelves, and other similar types of devices, often take the form of a large chassis or unit, sometimes weighing 50 to 100 lbs. or more. The chassis, sometimes referred to as a "shelf", typically incorporates one or more printed circuit boards or, more commonly, modular cards, with such cards typically being capable of being manually inserted and removed from the chassis. These printed circuit boards and/or cards incorporate semiconductor-based electronic components such as microprocessors and integrated circuit chips that generate significant amounts of heat during operation of the device.
Integrated circuit chips, microprocessors, and other similar electronic components are designed to operate within a particular temperature window. Accordingly, the heat generated by such components must be removed from the chassis or else the components will overheat and fail. It is known in the art to provide air flow features by which relatively cooler ambient air is conducted into the chassis, and relatively warmer air generated inside the chassis is exhausted from the chassis though an aperture in the chassis housing, typically using one or more fans. Representative patents addressing cooling and air flow considerations within an electronics device include the following references: Manes, U.S. Pat. No. 4,502,099, Garner, U.S. Pat. No. 4,648,007 and the patents to Gourdine, U.S. Pat. Nos. 5,297,005 and 5,422,787. Gourdine's patents describe a cabinet or chassis in which one or more electronic components are individually isolated and subject to separate airflow in order to maximize the cooling of all the components in the cabinet.
By making the aperture allowing heat to escape from the chassis larger, the capacity for cooling of the chassis is improved. Hence, large apertures are desirable. They allow increasing numbers of heat-generating components to be incorporated within the chassis and yet the chassis can operate within an acceptable temperature window.
In accordance with prior art techniques, there are limits and constraints on aperture size for warm air egress. The reason is that these types of telecommunications devices are also at least theoretically capable of catching fire should a short circuit or other type of malfunction occur in the electronic components. Various industry standards bodies frequently require that any fire that may break out within the device be contained within the device. While the semiconductor components themselves are not particularly flammable, epoxy and other materials used in the circuit boards are quite flammable. Should the chassis catch fire and the flames migrate out of the chassis, the room or building in which the chassis is installed is therefore also at risk of catching fire, a situation presenting an obvious hazard to life and property.
Patents directed to fire containment features for residences, and other types of buildings include the following references: Petit, U.S. Pat. No. 3,818,816 and Schaus, U.S. Pat. No. 4,805,835. However, to the inventor's knowledge, the art has never applied these teachings to communications or similar devices. One possible reason is that the complex problem of cooling, air flow, and fire containment in a telecommunication device or similar type of structure is quite different from fire containment issues pertaining to a dwelling, office building, or the like.
A chassis which on the one hand has a generous aperture for cooling purposes and good air flow characteristics, but which also provides features for preventing flames from migrating out of the chassis via the aperture, has apparently eluded the art. This invention provides features which not only allows for optimum cooling and air flow during periods of normal operation of the chassis, but also provides a fire containment feature which blocks the aperture to prevent fire or flames from escaping from the chassis and thereby provide increased safety for the device. As such, the present invention is believed to be a substantial advance in the art.
While the invention is described below in the context of one type of telecommunications chassis, namely a device terminating T1 spans in a telephone company central office, it will be readily apparent to persons skilled in the art that the invention is capable of wide application in other types of devices and the invention is certainly not limited to any particular type of communications device or chassis. For example, the invention could be incorporated into a personal computer or workstation. Thus, the scope of the invention is to be determined by reference to the appended claims. It is not intended to be limited to the example in the following detailed description. Hence the tern "chassis", as used in the specification and claims, is intended to encompass any unitary electronics device, such as a telecommunication or networking device, contained within a housing, regardless of the function performed by the device. The term chassis would therefore embrace, for example, a network access server, switch, router, T1 span termination shelf, workstation, personal computer, television set or any other similar type of device.